This invention relates to a printer for printing according to data sent from an external data source such as a computer. The previously used known printers for printing the output data from a computer and the like, usually print characters according to the character code sent from a computer connected thereto.
The setting of a margin, which is the starting position and the ending position of the printing of one line, is performed according to the steps mentioned below. First, an operator places a printing sheet on the platen of the printer, in such a manner that the left edge of the sheet meets with the left end of the platen. Next, the operator causes the printer to print characters stored therein. Then, the operator counts the number of characters existing between the left edge of the sheet and the left margin position and also counts the number of characters existing between the left edge of the sheet and the right margin position. The operator then enters special printing commands, which correspond to the numbers of characters previously counted, into the computer. The special printing commands corresponding to both margins are fed to the printer from the computer when the print commands are sent. As a result, the setting of the margins is completed.
After the setting of the margins, the printer prints the characters between the left margin position and the right margin position according to the margin data.
But, if the operator places a new sheet on the platen, and if the left edge of the sheet doesn't meet with the left end of the platen, the printing is not performed with the margin position at the expected location on the sheet. The printing is performed with the margin position shifted from the expected position because the margin position data doesn't indicate a distance from the left edge to the desired margin position of the sheet but rather indicates the distance from the left end position of the print area to the margin position of the sheet on the platen.
As stated above, in such a usual printer, in the case of a test printing for setting the margin, it is necessary to always set the sheet at the same position as the sheet used in the trial printing, for example, setting the left edge of sheet in accordance with the left end of platen. In addition, there is a big burden for the operator in that the operator must review the result of the trial printing and set the data of the margin position, and must transform the data into the special printing commands for the printer by way of the computer. It is impossible to set the margin in the case where the computer is in its operating mode since the margin setting is done by the computer. For example, in the case where the operater wishes to print the data calculated by the computer, even if the operator wants to change the margin, the operator cannot change the margin without stopping the computer program.